CP-CML patients who have received 2 or more calendar years of first-line imatinib treatment, and who have failed to achieve the molecular response threshold for treatment cessation (≥MR4.0) have a 50% greater chance of doing by switching to nilotinib; however the optimal duration of consolidation treatment with nilotinib to ensure the highest rate of patients remaining in ≥MR4.0 after entering the TFR phase is not yet known. This protocol therefore aims to assess the potential impact of a longer duration of consolidation treatment with nilotinib, i.e. 12 months versus 24 months, on molecular relapse rate in the first 12 months of treatment-free remission.